Method of impregnating leather and resultant article



Nov. 1, 1966 L. SELIGSBERGER METHOD OF IMPREGNATING LEATHER AND RESULTANT ARTICLE Filed Aug. 12, 1963 IMPREG/VATE FLESH SIDE OF LEATHER WITH AN INERT,

i ISCOUS, AQUEOUS SOLUTION.

IMPREGNATE GRAIN SIDE OF LEATHER WITH AN ORGAN/C SOLUTION CONTAIN/N6 AN INOOMPLETELY POLYMER/ZED POL YURE THANE CURE POLYURETHANE [MPREGNATED INGRA/N SIDE OF LEATHER TO FORM AN ELASTOMER/C SOL/D WASH INERT, V/SCOUS AOUEOUS SOLUTION FROM FLESH SIDE OF LEATHER LUDW/G SELIGSBERGER INVENTOR United States Patent METHOD OF IMPREGNATILIG LEATHER AND RESULTANT ARTICLE Ludwig Seligsberger, Newton Center, Mass, assignor to the United States of America as represented by the Secretary of the Army Filed Aug. 12, 1963, Ser. No. 304,715 11 Claims. ((11. 11768) The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

My invention relates to the impregnation of the grain side of leather with an incompletely polymerized polyurethane, which is further polymerized in situ to a rubbery vulcanizate after having penetrated into the 'interfiber space of the grain layer of the leather. More particularly, this invention involves impregnation of the grain side with a liquid composition containing as principal ingredients an incompletely polymerized polyurethane having a molecular Weight between about 750 and 10,000 and a porlyhydroxy containing crosslinking agent. Upon completion of the in situ curing of the polymer thus lodged in the interfiber spaces of the grain layer of the leather, there is obtained a supple leather the grain layer of which resists absorption and transmission of water, oil, petroleum fuels and is especially notable for its resistance to attack and penetration by chemical warfare agents. Leather impregnated according to this invention is characterized by a substantially higher abrasion resistance than untreated leather and has the additional desirable property of not stiffening at low temperatures.

Thus, an object of my invention is to provide a novel leather impregnating treatment producing a leather that resists penetration from the grain side of liquids such as water, petroleum products, liquid and gaseous chemical warefare agents, and corrosive liquids.

Another object of the invention is the impregnation of leather with a material which when introduced in the interfiber space of the grain side of the leather will permit the treated leather to be serviceable at low temperatures and will greatly increase the abrasion and scuff resistance of the leather.

A further object of my invention is to establish a leather treating procedure which is simple to perform, controls the depth of penetration of the impregnating liquid composition, and results in a quick cure of the impregnated material.

Other objects and advantages will be apparent from the fol-lowing description of my invention.

I am, of course, aware that it has been heretofore proposed to apply a finish coat to leather with polyurethane compositions to form hard, high gloss films thereon. Such coatings, which do not penetrate into the grain of the leather, however, are known to be brittle and because they tend to crack and to abrade offer no permanent solvent resistance. On the other hand my invention provides a method of treating leather with compositions designed to penetrate into the interfiber spaces and not form a surface coat. These compositions are applied to the grain side of the leather and as a result of a pre-treatment of the flesh side with a highly viscous non-reactive and preferably water soluble solution are confined to the grain layer. The result is a supple leather resistant to penetration by solvents and corrosive substances.

A leather impregnating composition for the purposes of my invention comprises a liquid mixture of from about 35 to 75 parts by weight and preferably from about 50 to 75 parts by weight of an incompletely polymerized 3,282,725 Patented Nov. 1, 1956 polyurethane, also known in the art as urethane prepolymers, capable of being cured to form an elastomeric solid and from about 5 to 30 parts by weight of a crosslinking agent containing free hydroxyl groups, preferably castor oil, other ricino-leic acid esters containing at least two ricinoleyl groups, codliver, fish, neatsfoot and tall oils either singly or in combination. These compositions are prepared by simply mixing in the presence of from about 20 to about 50 parts of an organic solvent not having an active hydrogen in its structure such as toluene, xylene, methyl ethyl ketone, carbon tetrachloride, perchlorethylene, Solvesso No. 100, Stoddard solvent and similar solvents or mixtures thereof to achieve a composition preferably having a viscosity of from about 300 to about 3,000 centistckes (Ostward-Cannon-[Fenske visc-osimeter at 86 F.)

Among the incompletely polymerized polyurethanes (urethane prepolyrners) suitable for use in my invention are the isocyanate terminated prepolymers having a molecular weight in the range between about 750 and about 10,000 and capable of being cured to hard elastomeric solids. The .prepolymers are prepared by reacting an excess of organic polyisocyanate with hydroxyl containing polyethers, polyesters, glycerides and castor oil. Typical organic polyisocyanates include tolylene diisocyanate, toluene 2,4-diisocyanate, hexamethylene =diisocyanate, triphenylmethane triisocyanate, m-pheny-lene diisocyanate, diphenylmethane 4,4 diisocyanate. Suitable polyethers include the polyalkylene ether glycols having a molecular weight above 750, e.g., polyethylene ether glycol, polypropylene ether glycol, polytetramethylene ether glycol and polydecamethylene ether glycol. Polyesters include polyal kylene esters of alkylene or arylene diacids and esters of polyhydric alcohols and hydroxy fatty acids. The preparation of typical prepolymers is disclosed in US. Patents 2,929,800 and 2,333,639.

The grain side of leather treated in accordance with my invention resists penetration by water, petroleum products and corrosive liquids. By limiting the urethane polymer to the grain side the flesh side remains highly water absorbent which is a significant comfort factor in articles of clothing such "as shoes, gloves, etc. Impregnation of the grain layer with polyurethane does not stiffen the leather whereas complete impregnation of flesh and grain layers greatly decreases the flexibility of the leather.

In order to prevent penetration of the impregnating composition into the flesh side, a viscous aqueous solution of a thickening susbta-nce which does not react with leather, e.g., gelatine, polwinyl alcohol, carboxymethylcellulose, cellulose gum, is brushed on the flesh side of the leather until substantially all of the interfiber spaces of the flesh side have been filled. The viscosity of the solution must be such that the solution will penetrate the flesh layer but not the grain layer. This determination can readily be made by one skilled in the art and will vary with different types of leather. The urethane prepolymer solution is subsequently applied to the grain side and is confined to the grain layer because of the presence in the flesh layer of the viscous solution which is not miscible with the prepo-lymer solution. After the urethan-e prepolymer has been cured the viscous solution may, if desired, be removed by washing.

Leather containing a cured urethane polymer in the interfiber spaces as taught by my invention unexpectedly exhibits superior resistance to penetration by chemical warfare agents such as mustard gas, lewisite and chlorine. The prior art methods of reading leather resistant to chemical warfare agents requires that the grain and flesh layers be stuifed with a wax composition which adversely influences the durability and other desirable physical characteristics of the leather. In addition such treatments 3 are temporary and must be renewed. The impregnated leather of my invention provides a permanent barrier against all known vesicant agents.

Satisfactory results are attained when the impregnated leather contain from to more than 40 grams of polyurethane per sq. foot. While one application has been found to be sufficient for most glove and garment leathers, a second application may be necessary for shoe upper leather.

Leather impregnation in accordance with my invention is suitable for any type of tanned leather, e.-g., leather tanned by mineral, vegetable, aldehyde, synthetic tanning agents or combinations thereof and is suitable for leather prepared from any type of animal hide or skin.

Example I A 20 g. .per liter aqueous solution of polyvinyl alcohol was brushed onto the flesh side of chrome tanned cowhide glove leather until the weight of the leather had increased by about 60 grams per sq. ft.

A solution prepared by dissolving 300 g. Adiprene L-lOO (an isocyanate terminated urethane prepolyrner commercially available from E. I. du Pont de Nemours & Co., Wilmington, Delaware, having an isocyanate content of 4.2%, a viscosity range between 14,800 and 16,000 centipoises Brookfield at 86 F.), 60 g. castor oil, 40 g. codliver oil and 20 g. neatsfoot oil in a mixture of 140 g. perchlorethylene and 70 g. Stoddard solvent was brushed on the grain side of the leather until the Weight of the leather had increased by g. per sq. ft. The impregnated leather was cured for 48 hours at 140 F. The polyvinyl material was washed from the flesh side and the leather allowed to dry.

Water resistance was measured by the Quarter-master tap tester illustrated and described on pages 637 and 63 8 of the December 1956 issue of Journal of the American Leather Chemists Association. A sample of treated leather showed no water penetration when tapped 3600 times under a /2-lb. load Whereas an untreated sample of the same leather failed at between and 40 taps.

Jet fuel and gasoline failed to penetrate a specimen of the impregnated leather under the test conditions set fiorth in Journal American Leather Chemists Association 54, 93, 1959. A sample of the leather also showed excellent resistance to penetration by mustard gas vapor.

Example II A solution consisting of 70 parts of an isocyan-ate terminated urethane polymer (L-167, a product of I. E. du Pont & Co., having an iso-cyanate content of 6.36.4%, a Brook-field viscosity of 86 F. between 6,000 and 8,000 centipoises, a molecular weight of approximately 750, and a specific gravity of 1.06 at 75 F.), 15 parts castor oil, 10 par-ts co-dliver coil and 5 parts neatsfoot oil in 67 parts perchlorethylene and 33 parts Stoddard solvent was prepared and after 3 hours had a viscosity of approximately 1,200 centistokes.

The hesh side of a deeply bufied chrome upper leather was treated with a viscous solution of carboxymethylcellulose (10 gm. per liter of water) until the weight was increased by g./ sq. ft.

Two coats of the impregnating solution were brushed on the grain side of the leather specimens which were then cured for 40 hours at 140 F. The total add-on was found to be 18.8 g./sq. ft. The leather exhibited excellent resistance to water, gasoline and mustard gas penetration.

Example III A urethane prepolymer was prepared by first heating 3 mols of ethylene glycol, 1 mol of 1,2-propylene glycol and 2.66 m'ols of adipic acid at 210-220" C. at a pressure of 1 mm. of Hg for about 12 hours to produce a viscous polyester. A 30% excess of 2,4-tolylene diisocyanate was added to the polyester and heated at 110 C. for 1 hour to produce the prepolymer.

An impregnating solution is prepared by dissolving 300 g. of the prepolymer, 60 .g. castoroil, 40 g. cod oil and 20 g. neatsfood oil in a mixture of 140 g. perchlorethylene and 70 g. Stoddard solvent.

A viscous solution containing 40 g. of gelatine per liter of water is brushed onto the flesh side of one square foot of deeply buffed chrome side upper leather until the weight of the leather has increased by 30 g. Immediately thereafter the prepolymer solution is brushed on the grain side to achieve a 40 g. pickup. The leather is cured at room temperature for 72 hours and then rinsed for 4 hours at 50 C. in order to remove the igelatine solution.

A dried specimen of washed leather resisted penetration of mustard gas vapor for 6 hours, demonstrated excellent resistance to penetration by Water, jet fuel, and gasoline.

Example IV parts of polytetramethylene ether glycol, molecular weight approximately 900, and 30 parts of toluene-2,4 diisocyanate are mixed and heated in a reaction vessel for 3 hours at 85 C. The resulting isocyanate terminated prepolymer analyzes 4.3% free isocyanate by weight.

A lukewarm solution of 20 g. carboxymethylcellulose in a liter of water was brushed onto the flesh side of deeply buffed chrome side leather until the weight of the leather has increased by 30 g. per square foot.

An impregnating solution was prepared by dissolving 15 lbs. of the prepolymer, 3 lbs. of castor oil, 2 lbs. cod liver oil and 1 lb. of neatsfoot oil in a mixture of 7 lbs. perch-lorethylene and 3 /2 lbs. Stoddard solvent.

This solution was brushed on the grain side of the leather until there was deposited approximately 30 grams per sq. ft. of solids based on the weight of the leather.

Leather sides so treated were hung at room temperature to cure for 48 hours and then rinsed for 4 hours at 50 C. to remove the carboxymethylcellulose. The leather was made mildew-proof by soaking with an 0.8% solution of paranitrophenol. The specimen was air dried and demonstrated excellent resistance to penetration by water, jet fuel and mustard gas vapor.

Example V A warm solution of 20 g. carboxymethylcellulose in a liter of Water was brushed on the flesh side of a 1 sq. ft. piece of deeply buffed chrome leather until the weight of the flesh layer had increased by 60 g. thereby substantially filling the interliber spaces of the flesh layer.

A solution was prepared by dissolving 125 g. Spenkel P 93-80X (an isocyanate terminated polyurethane prepolymer commercially available from Spencer Kellogg and Sons, Inc., B-ulfalo, New York, having a viscosity of 1,000 poises, and acid value of 1.2, specific gravity 1,023, and 7.7% available isocyanate in 20% xylol) 20 g. castor oil, 10 lg. cod oil and 5 g. neatsfoot oil in 75 g. Solvesso No. 100. This solution was applied in two coats to the grain side of carboxymethylcellulose impregnated leather. The leather was then held for 3 days at room temperature to complete the cure. The cured leather was rinsed in water of -125 F. to remove the carboxymethylcellulose.

The impregnated leather of this example provided excellent protection against mustard gas.

For purposes of graphically set-ting out the process of the present invention, reference is made to the accompanying drawing, which illustrates a flow sheet of the leather treating process of this invention.

The invention described in detail in the foregoing specification is susceptible to changes and modifications as may occur to persons skilled in the art without departing from the principle and spirit thereof. The terminology used in the specification is for purpose of description and not of limitation, the scope of the invention being defined in the claims.

I claim:

1. A method of treating leather having flesh and grain layers which comprises:

(a) impregnating said leather from the flesh surface inwardly with an aqueous solution of a thickening agent which will not react with the leather, said aqueous solution having a viscosity which will allow the solution to penetrate into and substantially fill the inter-fiber spaces of the flesh layer but not penetrate into the smaller inter-fiber spaces of the grain layer,

(b) subsequently impregnating the leather, while the inter-fiber spaces of the flesh layer are still impregnated with the aqueous solution of the thickening agent, from the grain surface inwardly to substantially fill only the inter-fiber spaces of the grain layer with an organic liquid composition comprising (1) an isocyanate-terminated urethane prepolyrner having a molecular weight between 750 and 10,000,

(2) a polyhydroxy containing cross-linking agent capable of cross-linking said prepolymer to an elastomeric solid and (3) an organic solvent not having an active hydrogen in its structure, said organic liquid composition being immiscible with said aqueous solution,

(c) and then curing said urethane prepoly-mer in the inter-fiber space of said grain layer to form an elastomer; whereby a flexible, impregnated leather is obtained that is resistant to penetration by water, petroleum products and vesicant gasses.

2. The method of claim 1 wherein said organic liquid composition has a viscosity between about 300 and 3,000 centistokes.

3. The method of claim 2 wherein at least grams of polyurethane elastomer are deposited in each square foot of leather so treated.

4. The method of claim 3 wherein the thickening agent added to water is selected from the group consisting of gelatin, polyvinyl alcohol carboxyrnethylcellulose and cellulose gum.

5. The method of claim 4 with the additional step of 6 washing the aqueous solution of the thickening agent from the flesh side after the urethane prepolymer has been cured in situ.

6. The method of claim 1 wherein said organic liquid composition comprises (a) from about 35 to 75 parts by weight of a liquid isocyanate-termin-ated urethane prepolyrner having a molecular weight of between 750 and 10,000,

(b) from about 5 to 30 parts by weight of a polyhydroxy cross-linking agent capable of cross-linkin-g said prepolymer to an elastorneric solid and (c) from about 20 to about parts by weight of an organic solvent not having an active hydrogen in its structure to produce a solution having a viscosity of from about 300 to about 3,000 cent-istokes.

7. The method of claim 6 wherein at least 10 grams of polyurethane elastorner is deposited in each square foot of leather so treated.

8. The method of claim 7 wherein the thickening agent added to the water is selected from the group consisting of gelatin, polyvinyl alcohol, carboxymethylcellulose and cellulose gum and wherein the polyhydroxy cross-linkir1g agent is selected from the group consisting of cast-or oil, ricinoleic acid esters containing at least two ricinoleyl groups, codliver oil, fish oil, neatsfoot oil, tall oil, and mixtures of the foregoing.

9. The method of claim 8 with the additional step of washing the aqueous solution containing the thickening agent from the flesh side after the urethane prepolymer has been cured in situ.

10. Leather produced by the method of claim 1.

11. Leather produced by the method of claim 7.

References Cited by the Examiner UNITED STATES PATENTS 1,203,303 10/1916 Bickett 117-68 X 2,159,704 5/1939 Levey 117-122 2,933,418 4/1960 Dogliotti et a1. 117-142 X 3,027,276 3/1962 Cohen et al 117-161 3,178,310 4/1965 Berger et a1 117-142 MURRAY KATZ, Primary Examiner. 

1. A METHOD OF TREATING LEATHER HAVING FLESH AND GRAIN LAYERS WHICH COMPRISES: (A) IMPREGNATING SAID LEATHER FROM THE FLESH SURFFACE INWARDLY WITH AN AQUEOUS SOLUTION OF A THICKENING AGENT WHICH WILL NOT REACT WITH THE LEATHER, SAID AQUEOUS SOLUTION HAVING A VISCOSITY WHICH WILL ALLOW THE SOLUTION TO PENETRATE INTO AND SUBSTANTIALLY FILL THE INTER-FIBER SPACES OF THE FLESH LAYER BUT NOT PENETRATE INTO THE SMALLER INTER-FIBER SPACES OF THE GRAIN LAYER, (B) SUBSEQUENTLY IMPREGNATING THE LEATHER, WHILE THE INTER-FIBER SPACES OF THE FLESH LAYER ARE STILL IMPREGNATED WITH THE AQUEOUS SOLUTION OF THE THICKENING AGENT, FROM THE GRAIN SURFACE INWARDLY TO SUBSTANTIALLY FILL ONLY THE INTER-FIBER SPACES OF THE GRAIN LAYER WITH AN ORGANIC LIQUID COMPOSITION COMPRISING 